The field of flame retardant raw materials is currently undergoing rapid expansion and intensive development as the emphasis on safety is steadily increased and government regulations are made more stringent and expanded to cover additional industries and products. As a result many improvements have been made in coating materials to enhance their flame retardant character and performance. Most of these improvements have involved the incorporation of additional ingredients, component modifiers or synergistic combinations of same leading steadily to increasingly complex formulations, more complicated processing and concomitantly increasing costs.
For example, in attempting to enhance the flame retardancy of latex bases for coating applications such as carpet backings, the major prior art approach has been to include appreciable amounts of halogen containing monomers in a complex monomer mixture which is all polymerized together to form an elastomeric latex. Representative prior art disclosures illustrating this basic approach are found in U.S. Pat. Nos. 3,546,059 to Isgur et al. and 3,962,170 to Mally wherein vinylidene chloride is the halogen containing monomer and it is copolymerized with at least an equal amount by weight and generally more of at least three other monomers chosen mostly from conventional elastomeric comonomer combinations, such as butadiene (or any other diene) plus styrene (or acrylonitrile) together with minor amounts of such functional monomers as unsaturated carboxylic acids. The resulting complex copolymer latexes evidently function well as flame retardant binders for coating carpets and other flexible substrates. However, the multicomponent copolymerizations employed therein are inherently complicated and require intricate measures are careful control in order to obtain uniform products. In fact, a study of the working examples in said patents reveals that considerable amounts of the monomers (about 10% or more) remain unreacted even after extended polymerization runs (e.g. 10 hours or even longer). Therefore, special monomer removal steps and finishing treatments would be necessary to produce commercially acceptable latexes from such prior art polymerizations.
Accordingly, a major object of this invention is to produce strongly flame retardant latex bases in a highly efficient and economical manner. Fundamental to this object is the performance of the necessary polymerization reactions under simplified conditions insuring more complete monomer conversions and reduced overall polymerization cycles. A related object is to permit the polymerization involved to be regulated more closely and thus achieve more selectively and greater reproducibility in regard to the critical parameters of the finished products. Another object is to simplify monomer removal problems and reduce the finishing and purification costs otherwise incurred therefrom.
A special object is to provide stable latex bases of exceptional versatility and wide utility in highly flame retardant coating compositions, including those suited for use on carpets, fabrics and other flexible substrates.
Various other objects and advantages of this invention will be apparent from the complete description thereof which follows.